I. Field of the Invention
The present invention is directed generally to the field of sophisticated, high velocity, large or medium caliber projectile ammunition and, more particularly, to an improved geometric propellant loading configuration for such ammunition. The propellant system of the invention includes several mutually contiguous extrudable stick shapes that in concert result in highly efficient use of propellant load space. The system reduces loading, assembling and packing (LAP) labor and overall cost, yet provides a dense pattern to increase propellant load and high perforation to improve burning progressivity over prior stick loads and more reliable and improved ballistic performance.
II. Related Art
The technology of large and medium caliber ordnance generally has evolved into the use of increasingly sophisticated projectiles and firing systems. Smaller diameter projectiles are often used together with discarding sabots that transfer momentum to the projectiles which develop very high velocity (Mach V+) and so very high kinetic energy (KE). The projectiles themselves have also become more aerodynamic and generally employ a plurality of stabilizing fins. These so-called munitions also may contain sophisticated highly sensitive target proximity detection devices which operate precision arming and detonating circuits. In addition to the electronic control and sensing improvements, the construction of the rounds themselves has undergone an evolution that has produced vastly improved capabilities in terms of the effect produced by a single round on a target.
Conventional ammunition of the class described, such as that fired by military tank cannons, are typically breech loaded and electrically activated and fired from within the tank. The projectiles typically are fired electrically using a primer circuit to ignite a primer which, in turn, ignites a main propellant charge by DC voltage from a thermal battery activated by the primer. The projectile may contain electronics activated when firing occurs and which utilize memory storage to operate a preprogrammed target acquisition or proximity system and the arming and detonating devices in the shell during the flight of the shell. Then, it is apparent that large caliber ammunition, with respect to target acquisition, proximity detection, arming and detonating, has become very sophisticated.
While all these developments are interesting and important to the advancement of the art, the success of all ammunition projectiles still depends greatly upon the performance, and reproducibility of the performance of the associated propellant system. A variety of techniques have been tried in order to improve ammunition muzzle velocity by increasing propellant charge density, i.e., increasing the amount of propellant per available cartridge volume unit and/or the progressivity of the burn by providing an ever increasing surface area. These techniques have included utilizing various preformed shapes packed into the cartridge in an effort to increase density while minimizing adverse effects on burning rate. Such techniques have included the use of various sizes of granular extruded (short grain) propellant shapes, perforated stick extruded shapes which are long and cylindrical or hexagonal in external geometry and represent the most commonly used stick shapes. These sticks are commonly provided with 7 or 19 longitudinal perforations (7 P or 19 P).
Several configurations of slab and disk-shaped propellant geometries are illustrated in co-pending application Ser. No. 08/537,882, filed Apr. 10, 1996, now U.S. Pat. No. 5,712,445, issued Jan. 27, 1998, and assigned to the same assignee as the present application, the contents of which are deemed incorporated by reference herein for any purpose. Another configuration is in the form of a rolled sheet of propellant. Bulk liquid propellants have also been used; however, they tend to burn in a non-reproducible manner and, therefore, results have been unpredictable.
FIG. 1 depicts a typical large caliber round, which may be fired from the main turret cannon of a tank or other artillery piece, loaded with propellant of one prior art type. The round is shown generally at 10 at FIG. 1 and includes a base plate section 12 connected with the wall of a cartridge casing and having a generally cylindrical portion 14 and a necked down or tapered upper portion 16. Except for the base plate 12, the shell or cartridge sidewall 14 itself is normally made of a combustible material such as molded nitrocellulose or other such material itself consumed during the firing of the shell. A projectile is shown at 18 with discarding sabot members 20 and 22 which peel away and drop off just after the projectile is discharged from the muzzle of the cannon. A plurality of stabilizing guidance fins (normally six in number) as at 24 are also provided. The nose cone section 26 may contain an electronics package and the warhead section 28 may contain arming and detonating circuitry.
With respect to the firing of the shell, a primer housing shown generally at 30 contains a conductive ignition electrode or primer button (not shown) and stub base 31. The primer housing and stub base are connected with a generally hollow brass or other type metal center-core primer tube 32 which has a plurality of openings as at 34 which access and address the general propellant charge volume 36. The propellant illustrated consists of closely packed, generally uniformly shaped, perforated, granular solid propellant grains 38 (FIG. 1B) perhaps 2 to 3 cm long by about 0.5 cm in diameter.
The shell is normally fired electrically using direct current to ignite the primer in the primer housing and through the primer tube 32, thereby igniting the main propellant 38 via the openings 34. In accordance with an important aspect of performance, i.e., achieving the highest, repeatable muzzle velocity for the projectile, however, it is desirable that the propellant, during the burn, generate gases at an ever increasing rate as the projectile advances along the barrel. Accordingly, a configuration of propellant which creates predictably and ever increasing burn surface area as the burn progresses is very desirable.
The present standard is based on the performance of stick propellant, particularly the round extruded stick shape which has increased shell velocities over earlier propellant loadings. However, a great many relatively small diameter sticks must be used, and the stick propellant has also presented difficulties with respect to achieving high loading density (FIGS. 2A, 2B, 3).
The loading process for a cartridge using stick propellant is also very labor intensive and performance is not optimum because adjacent surfaces of the sticks do not match, as in the case of random placement with granular propellant. The method used to extrude both stick and granular propellant includes pins that create perforations during the process. With sticks of present size (below), this method may create perforation and web inconsistencies which actually reduce the propellant performance.
Repeatability of acceptable or good performance of stick propellant also requires uniformity of the notch or kerf size and web between the kerfs for proper burning. The current processes of extrusion and kerf cutting are rarely able to achieve this so that the sticks must be blended or mixed prior to loading to achieve some uniformity. As a result of mixing the stick propellant, performance is not optimized.
FIGS. 2A and 2B are partial sectional views to illustrate prior art loading geometries for propellant sticks for a 120-MM shell 40 including a projectile 42 with six stabilizing guidance fins 44. Note that, although the slightly larger diameter (.O slashed.=0.657 in. 16.69 MM) sticks 46 of FIG. 2A better fill the outer periphery than the smaller (.O slashed.=0.625 in. 15.88 MM) sticks 48 of FIG. 2B, they leave larger voids about the fins and round sticks cannot accommodate both. Also, the interstitial void area is significant with round sticks in general.
FIG. 3 is a further schematic drawing that illustrates a vertical crossection of a fragment of a similar shell 50 without the baseplate containing projectile 52 with fins 54 and an ignition system as shown at 56. The loading of the cartridge 50 as can be seen from FIG. 3 requires at least eight different sizes or lengths of stick propellant (A-H) and in large quantities. Loading is by necessity labor intensive.
While perforated stick propellant provides configurations that yield high performance burns, as can readily be appreciated from the drawings, the loading of the shell also leaves considerable void space in the load. Perfect loading still leaves about 22% void space not counting perforations or kerf cuts.
Another method utilizing ribbed sheet propellant rolled into cylindrical sections has been tested on smaller caliber ammunition. This method used longitudinal ribs replacing perforations to assist ignition. The rolled method experienced difficulty in conformance to the projectile geometry, poor progressivity, poor flame spread and poor ignition characteristics.
Accordingly, it is a primary object of the present invention to produce a propellant loading which combines an increased charge load density with highly progressive burning achieved at a lower production cost.
Another object of the invention is to produce a propellant geometric configuration that uses fewer, larger grain shapes.
A further object of the invention is to provide a dense propellant loading geometry that enables convenient and efficient assembly of propellant within a straight or necked-down cartridge.
Yet another object of the invention is to provide a method of loading a propellant which uses a highly accurate, repeatable geometric shapes capable of sustaining high perforation density.
Other objects and advantages will appear to those skilled in the art in connection with familiarity with the descriptions and accounts of the invention in the following specification and drawings.